The present invention is directed to catheters and methods of manufacturing the same. In particular, the present invention is directed to soft tip catheters.
Catheters are used in various types of surgical procedures. For example, catheters may be used to deliver solutions to specific bodily areas, e.g for coronary angiography, or are constructed to act as guideways through which other catheters are directed to specific body locations. Irrespective of their ultimate usage, catheters are inserted and pushed through a particular a body vessel, e.g. a blood vessel. In order to easily pass through such a vessel the catheter is constructed to exhibit certain physical characteristics. That is, the catheter must possess specific physical properties to facilitate the insertion and passage through the vessel.
More particularly, the catheter should possess sufficient strength without being too stiff to facilitate the passage of the catheter through the vessel. Generally, a catheter is pushed through a vessel by twisting the catheter which moves the catheter along the vessel by a recoilling motion. Thus in order to facilitate this twisting movement through the vessel the catheter must have longitudinal flexibility, while also being somewhat rigid to provide for a high degree of torsional control.
While a rigid catheter provides the desired high torsional control, this rigidity of the catheter increases the potential of damaging the vessel as it travels through the vessel. In particular, the distal end, or tip, of a rigid catheter may puncture, or in some other manner damage the vessel through which it is travelling, or may cause damage to an organ in which it comes into contact.
Accordingly, catheters have been designed to possess a soft or flexible distal tip. This flexible tip minimizes the potential of damaging an organ or vessel by the catheter, while the rigid catheter body ensures movement through the vessel. Examples of such soft tip catheters ar well known.
One such soft tip catheter is disclosed in U.S. Pat. No. 4,402,684 issued to Jessup, wherein the catheter is formed with a soft outer sheath defining a lumen in which a stylete is positioned. This stylete subdivides the lumen into multiple pathways. By forming the stylete from a rigid polymeric material the desired rigidity is imparted to the catheter, while the outer surface of such a catheter remains soft to minimize damage to the vessel or organs it comes into contact with. However, the disclosed catheter is not suitable for forming a guide catheter in that the guide catheter lumen must remain open and thus could not contain the rigid stylete.
Other types of presently available soft tip catheters are manufactured by fusing a flexible tubular member to the distal end of the rigid catheter body. Examples of these types of catheters are disclosed in U.S. Pat. Nos. 4,563,181 issued to Wijayarathna et al; 3,485,234 and 3,585,707 both issued to Stevens; 4,321,226 issued to Markling; 4,531,943 issued to Van Tassel et al; and 4,665,604 issued to Dobowik. This type of catheter is also disclosed in U.S. patent application Ser. No. 946,491, filed on Dec. 23, 1986, and assigned to the same assignee of the instant application.
All of the catheters disclosed in this various patents fuse the soft tip to the end of the catheter body, typically using a lap joint fusing process, as disclosed in Markling, Dubowik and Stevens. While these types of catheters are advantageous in providing a soft distal tip for insertion into the vessel first, such catheters do possess certain disadvantages.
The basic disadvantage with these presently available catheters is the incompatibility between the polymers forming the soft pliable tip portion and the catheter body. This incompatibility reduces the resulting joint between the two fused together portions, even when the catheter is construction using a lap joint. This weak joint results from the incompatibility between the polymeric materials forming the catheter body and tip portions. That is, the body portion, is formed from a rigid polymer, while the tip portion is formed from another more elastic polymer, with these two different polymers reducing the bonding between the two portions to such a degree that even when the body and tip portions are properly bonded together a relatively weak joint results.
This particular disadvantage caused by the use of two different polymers was specifically recognized in Wijayarathna et al. This patent specifically discloses a tip formed from a polyether-polyamide material which is at least partially compatible with the polyamide (nylon) material forming the catheter body. The polyamide constituent of the polyether-polyamide material used to prepare the tip portion increases the bonding between the two portions, but still does not provide the type of bonding which would result from using the same two materials.
The major reason for existence of this type of disadvantage is that those polymers which have the characteristic of forming a rigid structure are not suitable for forming a soft catheter tip. As a result other methods of forming catheters to possess a soft tip have been developed to overcome the weak joint formed between the catheter tip and body portion with the above discussed catheters.
One particular method involves forming the catheter with two sheaths, an inner sheath formed from a rigid material and an outer sheath formed from a more flexible material. By extending the outer sheath beyond the inner sheath the catheter is provided with an integral soft tip. Examples of such catheters is disclosed in U.S. Pat. Nos. 4,239,042 issued to Asai and 4,596,563 issued to Pande.
Another type of catheter construction is disclosed in U.S. Pat. No. 4,636,346 issued to Gold et al. This catheter includes three sheaths, and inner sheath formed from polytetrflouroethylene (PTFE), an intermediate sheath formed from a rigid polymeric material and an outer sheath formed from a more flexible polymeric material. In order to form a more flexible tip portion the intermediate sheath is removed from the distal portion of the catheter. The disadvantage with this catheter design is that the PTFE inner sheath does not form an adequate bond with the outer sheath, thus forming a weak joint which may fail.
The major concern with the weak bonding joint found in the above discussed catheters is that failure along the fused joint between the catheter tip and body portions, while the catheter remains in the patient's body has obvious determental consequences to the patient. However, any proposed catheter construction must also maintain a soft tip portion, which heretofore has ruled out the use of rigid polymeric polymers in the tip area.